RSA Uncovers Ultra-Targeted "Bouncer List" Phishing Attacks

Researchers from EMC’s RSA Security division have identified a new phishing technique, which targets a very specific group of victims in targeted attacks.

"Bouncer list phishing" refers to how attackers focused the campaign to steal credentials from a pre-determined list of victims, Limor Kessem, cybercrime and online fraud communications specialist at RSA, wrote Tuesday on the RSA FraudAction Research Labs blog.

Attackers using this "unusual" kit began with a list of email addresses and assigned a unique user ID to each of the targeted recipients. When a user clicked on the attack URL, the kit first validated the ID to determine whether the user was on the list of victims being targeted. Those who failed validation never saw the phishing page, Kessem wrote.

Attackers would primarily adopt this technique in order to gain "quality" data by focusing on desirable victims, Daniel Cohen, head of business for online threats, told SecurityWeek. While RSA has seen campaigns filtering out victims before, the older methods generally used IP addresses to separate victims by geographic region. This is the first time an "invitee list was brought into play," Cohen said.

"Much like many high-profile nighttime hotspots—if your name is not on the list, you're staying out!" Kessem said.

When victims attempt to access the phishing page, the kit validates the ID "on the fly" to ensure the user is on the list. Only the unfortunate victims who make the cut get directed to the phishing page; "unintended visitors" are shuffled off to a "404 page not found" page, Kessem said. The kit doesn't even bother to generate the attack page for the unwanted visitors.

As soon as the bouncer kit identifies a desirable victim, it copies pertinent files into a temporary folder on the same Web server as the original attack website and loads the phishing page. After harvesting the credentials, the victim is redirected to yet another hijacked website.

RSA researchers have observed attacks using the bouncer list phishing against a South African financial institution and other organizations in Australia and Malaysia, Cohen said. The attack against the South African company targeted only users with email addresses on the .co.za domain, Cohen said.

Each campaign targeted an about 3,000 victims on average, with lists composed in alphabetical order, Kessem said. There were separate lists for emails beginning with each letter of the alphabet. Victims were a "mixed bag," and included webmail users, corporate addresses, and even some bank employees. It is likely the target list was compiled by aggregating a few spam lists or data breach collections, Kessem said.

"These kits, used to target corporate email recipients, can easily be part of spear phishing and the foothold of a looming APT-style attack," Kessem warned. This phishing method varies from traditional campaigns because attackers are not casting as wide a net as possible. Instead, the phisher is "laser-focusing" the campaign to collect specific credentials and data.

"Obviously quality data fetches a higher price in the underground," Cohen said. It was likely these attacks were the work of a service vendor and not a lonely phisher, he said.

RSA has noticed that phishing toolkits are increasingly becoming more complex and sophisticated, featuring new capabilities such as real-time credential validations and built-in Web analytics tools to gauge the campaign's success. Many of the kits take advantage of vulnerabilities in content management systems and third-party components. The new bouncer-list function was a perfect example of the trend, Kessem said.

The fact that a phishing page can display a 404 error page for some users "could present a detection challenge for the industry," Kessem said.

According to RSA, the total number of phishing attacks launched in 2012 was 59% higher than the total calculated for 2011, up from 279,580 attacks to 445,004, costing the global economy over $1.5 billion dollars in fraud damages.

Fahmida Y. Rashid is a Senior Contributing Writer for SecurityWeek. She has experience writing and reviewing security, core Internet infrastructure, open source, networking, and storage. Before setting out her journalism shingle, she spent nine years as a help-desk technician, software and Web application developer, network administrator, and technology consultant.